1. Field of the Invention
This invention relates to an automatic washing machine, and more particularly to an improvement in a power transmission mechanism for transmitting torque developed by an electric motor to a rotating tub and an agitator in such an automatic washing machine.
2. Description of the Prior Art
An automatic washing machine having a dehydrating function comprises a rotating tub serving both as a washing tub and as a dehydrating tub and an agitator mounted on a bottom of the rotating tub. Torque developed by a drive motor is transmitted only to the agitator in a wash step, whereas the motor torque is transmitted both to the agitator and to the rotating tub in a dehydration step. Japanese Patent Application Publication No. 10-52595 (1998) discloses one of power transmission mechanisms transmitting the motor torque selectively only to the agitator or both to the agitator and to the rotating tub.
In the transmission mechanism disclosed by the above mentioned publication, the rotating tub is rotated via a hollow dehydration shaft, and the agitator is rotated via a wash shaft extending through the dehydration shaft. A vertically movable connecting gear mechanism or clutch is provided for connecting the dehydration and wash shafts to each other and disconnecting the shafts from each other. The connecting gear mechanism is vertically moved via a number of parts including rotating gears, lifting gears, a lifting ring, a lifting guide plate, etc. These parts complicates the construction of the connecting gear mechanism.
On the other hand, Japanese Utility Model Publication No. 6-42630 (1994) discloses another transmission mechanism comprising a hollow dehydration shaft provided for rotating the rotating tub and a wash shaft extending through the dehydration shaft and provided for rotating the agitator via a reduction gear mechanism. The wash shaft has a lower end connected to a boss of a pulley to which the motor torque is transmitted. A lower end of the dehydration shaft has a guide groove formed in an outer circumferential face thereof. The boss of the pulley also has an upper end with a guide groove formed in an outer circumferential face thereof. A cylindrical cap (clutch) is provided so as to be vertically moved along the guide grooves. The cap is vertically moved by a lever.
In the aforesaid construction, however, a large torque is transmitted from the boss via the cap to the dehydration shaft. Accordingly, when the cap, boss and dehydration shaft have respective portions which engage the guide grooves and have small vertical dimensions respectively, an inner circumferential surface of the cap is subjected to an excessive force such that the cap is deformed or broken. As a result, the portion of the cap engaging the guide grooves needs to have a large vertical dimension, whereupon the size of the overall cap is increased vertically, and an amount of vertical movement of the cap is increased. Consequently, the size of the transmission mechanism is increased.